Melt-molding metallurgical method

ABSTRACT

A melt-molding metallurgical method includes the steps of: (A) preparing raw material powder and a binder material; (B) mixing the raw material powder and the binder material to obtain pellets; (C) pressing the pellets to obtain a solid state material; (D) preparing a molding device which includes a conveying unit and a forming space; (E) activating the conveying unit; (F) heating the solid state material to become a liquid state material; (G) driving the solid state material that has not melted to push the liquid state material into the forming space; (H) cooling the liquid state material to solidify the same into a blank; (I) debinding the blank; and (J) sintering the blank.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese Patent Application No.109137132, filed on Oct. 26, 2020.

FIELD

The disclosure relates to a molding process, more particularly to amelt-molding metallurgical method.

BACKGROUND

In order to produce metal workpieces, the most traditional processingmethod is casting. Casting is a process in which a metal material ismelted into liquid at a high temperature, and then the liquid is pouredinto a mold and cool to solidify. In casting, it is not only necessaryto heat the material to a high temperature, but also the temperature ofthe material must be maintained before being injected into the mold.Further, the mold must also be able to withstand the corresponding hightemperature in order to form the material. Moreover, the danger causedby high temperature must also be considered, so that correspondingsafety facilities must be set up. Therefore, the technology of “powdermetallurgy” was developed in modern times. Powder metallurgy is aprocess in which metal powder is put into a mold and then press into ablank. The blank is preformed into the appearance of a workpiece, butthe structural strength is still quite low. Thus, it is necessary toperform sintering on the blank in order to improve the structuralstrength thereof. The advantage of using the powder metallurgy is thatit is not necessary to heat the metal material to a liquid state, aslong as it reaches the recrystallization temperature. Further, theaforesaid problems of maintaining the temperature of the material, themold being able to withstand the corresponding high temperature, and thedanger of high temperature can be eliminated.

In recent years, the technology of powder metallurgy and plasticinjection molding are combined to form metal injection molding (MIM). Inthe metal injection molding process, powdered metal is injected into amold using an injection machine, and then sinter it after forming in themold. In comparison with the traditional powder metallurgy, the metalpowder used in the metal injection molding is finer, so it has fluidityand can be injected by an injection machine. Further, because of thefiner metal powder, a denser metal structure can be obtained aftersintering. Therefore, the application of the metal injection moldingtechnology can produce high density, high precision and complex-shapedmetal workpieces. However, the metal injection molding still has thedisadvantage of not being able to manufacture large workpieces. This isbecause the fluidity of metal powder is still poor compared to fluid. Inaddition, based on the characteristics of injection molding, the valueof maintaining pressure can only be used as a control parameter tocontrol the injection volume, and it is impossible to accurately adjustthe injection volume for different numbers and sizes of mold cavities.

All of the aforesaid technologies require the injection of liquid metalor metal powder. Therefore, the mold must be provided with a sprue orrunner. After the material is formed, the material remaining in thesprue or runner will become a scrap. In order to remove the scrap,additional processing must be performed after the material hassolidified or sintered. For example, most of the scrap is first removedby cutting, followed by polishing and grinding to obtain a smoothsurface. It should be noted that the scrap cannot be cut beforesintering. Because the structural strength of the blank before sinteringis quite low, if the shearing is performed, other adjacent parts maycollapse and disintegrate. On the other hand, the structural strength ofthe blank after sintering becomes quite high, so that it is quitedifficult to remove the scrap.

SUMMARY

Therefore, an object of the present disclosure is to provide amelt-molding metallurgical method that has good fluidity, that requiresno additional processing and that can precisely control injection volumeand injection speed.

Accordingly, a melt-molding metallurgical method of this disclosureincludes the following steps: (A) preparing raw material powder and abinder material; (B) mixing the raw material powder and the bindermaterial to obtain pellets; (C) pressing the pellets to pass through aneye mold so as to obtain a solid state material; (D) preparing a moldingdevice, the molding device including a conveying unit disposeddownstream of the eye mold for conveying the solid state material alonga conveying direction, a heating unit disposed downstream of theconveying unit along the conveying direction, and a molding unit, theheating unit including a main body, a nozzle disposed on a downstreamside of the main body, and a heating channel extending through the mainbody and the nozzle for passage of the solid state material therein, themolding unit including at least two molds that cooperate with each otherto define a forming space, the nozzle having an injection portcommunicating with the heating channel; (E) activating the conveyingunit for conveying the solid state material from the eye mold to theheating channel; (F) heating the solid state material to melt a portionof the solid state material that is proximate to a forming space andbecome a liquid state material; (G) driving the solid state materialthat has not melted to push the liquid state material into the formingspace; (H) cooling the liquid state material in the forming space tosolidify the same into a blank; (I) debinding the blank for removing thebinder material from the blank; and (J) sintering the blank to obtain afinished product.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the disclosure will become apparent inthe following detailed description of the embodiment with reference tothe accompanying drawings, of which:

FIG. 1 is a flow chart, illustrating the steps involved in amelt-molding metallurgical method according to an embodiment of thepresent disclosure;

FIG. 2 is a conceptual diagram of FIG. 1;

FIG. 3 is a schematic view of the structure of an eye mold and a moldingdevice of the embodiment; and

FIG. 4 is a view similar to FIG. 3, but with two molds being separatedto permit removal of a blank.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, a melt-molding metallurgical methodaccording to an embodiment of the present disclosure includes steps S1to S10, and will be described in detail below with reference to FIGS. 3and 4.

In step S1, raw material powder and a binder material are prepared. Amelting point of the binder material is lower than that of the rawmaterial powder. In this embodiment, the raw material powder is glasspowder, but is not limited thereto, and may be metal powder, glasspowder or ceramic powder. Further, the binder material is a crosslinkingagent. Common crosslinking agents include white wax, polyurethane,acrylate, etc.

In step S2, the raw material powder and the binder material areuniformly mixed to obtain pellets. How to perform mixing and obtain thepellets is well known to the person having a common knowledge in thisfield, and is not an important aspect of this disclosure, so that adetailed description thereof is omitted herein.

In step S3, the pellets are pressed to pass through an eye mold 1 so asto obtain a solid state material (R). The solid state material (R) has alinear or rod shape. Specifically, the eye mold 1 has a narrow passage11. When the pellets are pushed by a considerable degree of pressure andpass through the passage 11, they will squeeze each other and heat up,so that the binder material portion in each pellet is softened or melted(while the raw material powder portion in each pellet remains solid),thereby binding the pellets together and form the solid state material(R).

In step S4, a molding device 2 (see FIG. 3) is prepared. The moldingdevice 2 includes a conveying unit 21 disposed downstream of the eyemold 1 for moving the solid state material (R) along a conveyingdirection (T), a heating unit 22 disposed downstream of the conveyingunit 21, and a molding unit 23 disposed downstream of the heating unit22. The conveying unit 21 may include two rollers (not shown)cooperatively clamping therebetween the solid state material (R). Inthis way, the moving distance of the solid state material (R), themoving speed of the solid state material (R), and the force of pushingthe solid state material (R) can be controlled by controlling therotational speed and the clamping force of the rollers. However, thisstructural design is just an example, and those skilled in the art maychoose other methods to push the solid state material (R) according tothe requirement, and is not limited to the aforesaid disclosure.

The heating unit 22 includes a main body 221, a nozzle 222 disposed on adownstream side of the main body 221, a heating tube 223 disposed in themain body 221, a heat source 224 embedded in the main body 221, and atemperature sensor 225 adjacent to the heat source 224. The nozzle 222is connected to the heating tube 223, and cooperates with the same todefine a heating channel 226 for passage of the solid state material (R)therein. The heating channel 226 extends through the main body 221 andthe nozzle 222. The nozzle 222 has an injection port 233 communicatingwith the heating channel 226.

It should be noted herein that, in this embodiment, only a portion ofthe heating tube 223 extends into the main body 221, so that a junctionof the nozzle 222 and the heating tube 223 is located inside the mainbody 221, but is not limited thereto. In other variations, the heatingtube 223 may extend through the main body 221, so that a junction of thenozzle 222 and the heating tube 223 is located outside the main body221.

The molding unit 23 includes two molds 231, 231′ that are mated in anup-down direction and that cooperate with each other to define a formingspace 232. The mold 231′ is disposed below the mold 231, and has aninsertion hole 236 for insertion therein of the nozzle 222 such that theinjection port 233 of the nozzle 222 is immediately adjacent to theforming space 232. The heating channel 226 communicates with the formingspace 232 through the injection port 233. In this embodiment, themolding unit 23 includes two molds 231, 231′, but is not limitedthereto, and may include three or more molds according to therequirement.

In step S5, the conveying unit 21 is activated to convey the solid statematerial (R) from the eye mold 1 to the heating channel 226.

In step S6, the heating unit 22 is activated so that the solid statematerial (R) in the heating channel 226 can be heated by the heat source224. When the solid state material (R) is heated, a portion of the solidstate material (R) that is proximate to the nozzle 222 will melt andbecome a liquid state material (L). It should be noted that the liquidstate material (L) is heated to a temperature between the melting pointof the binder material and the melting point of the raw material powder,so that the composition of the liquid state material (L) still containsthe raw material powder that has not been melted.

In this embodiment, the size of the heating channel 226 that isproximate to the injection port 233 is gradually reduced. As such, thepressure of the liquid state material (L) will gradually increase as itmoves toward the injection port 233, so that it can be injected into theforming space 232 via the injection port 233.

Further, the heat source 224 can be controlled through the temperaturesensor 225 so that the solid state material (R) can reach a sufficientlyhigh temperature and melt.

In step S7, after the conveying unit 21 and the heating unit 22 areactivated, the solid state material (R) that has not melted is driven bythe conveying unit 21 to push the liquid state material (L), so that theliquid state material (L) is injected into the forming space 232 fromthe injection port 233.

It is worth to mention herein that, in this embodiment, the step ofconveying the solid state material (R) to the heating channel 226 instep S5 is first performed, followed by step S6 and step S7 to achievethe state shown in FIG. 2. However, there is no particular limitation onthe sequence of step S5 and step S6, and can be executed sequentially,simultaneously, mixedly or repeatedly according to the requirement. Themolding device 2 can be operated manually or by automatic control.

In step S8, the molding unit 23 is cooled to cool and solidify theliquid state material (L) in the forming space 232 into a blank 3. Itshould be noted that after cooling, the molds 231, 231′ are separated toexpose the forming space 232 to thereby facilitate removal of the blank3.

In step S9, the blank 3 undergoes a debinding process to remove thebinder material from the blank 3. The debinding process may be a processof heating, water washing, solvent washing or a combination thereof.Those skilled in the art may select an appropriate technical meansaccording to different binder materials to achieve the purpose ofremoving the binder material from the blank 3.

In step 10, the blank 3 is sintered to obtain a finished product. Duringsintering, the microstructure of the blank 3 will change to improve itsstructural strength. Specifically, after the debinding process, theblank 3 is mainly composed of the raw material powder, but themicrostructure thereof is very loose, and the overall structuralstrength is weak. When heated above the recrystallization temperature(that is, during sintering), the grain boundary between molecules willdisappear, allowing the molecules to rearrange and recrystallize. Inthis way, the molecules in the blank 3 can produce an integratedmicrostructure, naturally increasing the strength of the structure ofthe blank 3, so that the blank 3 can become a finished product for sale.

In this embodiment, because the portion of the solid state material (R)that is proximate to the forming space 232 will melt and become theliquid state material (L), injected into the forming space 232 is alsothe liquid state material (L). Compared with the prior art, the liquidstate material (L) is a fluid so that it naturally has a better fluiditythan that of the powder. Therefore, this embodiment can be used to makelarger workpieces. Further, the maximum temperature required in thisembodiment only needs to reach the recrystallization temperature, noneed to reach the melting point of the raw material powder. The problemsencountered in the prior art, such as maintaining the materialtemperature, the mold must be able to withstand the corresponding hightemperature, and the danger caused by high temperature, can be avoided.

Furthermore, since the liquid state material (L) is directly injectedinto the forming space 232 via the injection port 233, the molds 231,231′ do not need to be provided with sprues or runners. Hence, the blank3 does not produce any scrap, so that the blank 3 becomes a finishedproduct after sintering, and no additional processing is required.

Moreover, the liquid state material (L) leaving the heat source 224 andgoing to the injection port 233 is gradually cooled. To prevent thematerial remaining in the heating channel 226 from solidifying due tothe cooling of the molding unit 23, after the injection is completed,the solid state material (R) can be conveyed in a reverse direction ofthe conveying direction (T) through the conveying unit 21, so that theliquid state material (L) near the injection port 233 can be drawn backand will not be solidified. The liquid state material (L) is pushedagain from the heat source 224 toward the injection port 233 in the nextprocessing. Thus, the liquid state material (L) can be properly used andthe effect of almost no waste can be achieved. Additionally, keeping theheat source 224 in an activated state not only can maintain the liquidstate material (L) at a certain temperature without solidification, butalso can facilitate continuous processing.

In addition, in this embodiment, the conveying unit 21 can be used notonly to control the force required to push the solid state material (R),but also to control the moving rate of the solid state material (R). Inthe prior art, the injection volume and the injection speed can only becontrolled by the maintaining pressure, so that this embodiment isdifferent from the prior art. Because the solid state material (R) has alinear or rod shape, the injection amount and the injection speed ofthis embodiment can also be estimated through the length of the solidstate material (R) that has been fed. Therefore, in comparison with theprior art, this embodiment can more accurately control the injectionamount and the injection speed.

In summary, in the melt-molding metallurgical method of this disclosure,the portion of the solid state material (R) proximate to the formingspace 232 will melt and become the liquid state material (L) which hasmore fluidity than powder. Further, the liquid state material (L) isdirectly injected into the forming space 232, so that the blank 3 canbecome a finished product after sintering, and no need for additionalprocessing. Moreover, not only the force required to push the solidstate material (R) can be controlled, but also the moving rate of thesolid state material (R) can be controlled so as to accurately controlthe injection amount and the injection speed. Therefore, the object ofthis disclosure can indeed be achieved.

While the disclosure has been described in connection with what isconsidered the exemplary embodiment, it is understood that thisdisclosure is not limited to the disclosed embodiment but is intended tocover various arrangements included within the spirit and scope of thebroadest interpretation so as to encompass all such modifications andequivalent arrangements.

What is claimed is:
 1. A melt-molding metallurgical method comprising:(A) preparing raw material powder and a binder material; (B) mixing theraw material powder and the binder material to obtain pellets; (C)pressing the pellets to pass through an eye mold so as to obtain a solidstate material; (D) preparing a molding device, the molding deviceincluding a conveying unit disposed downstream of the eye mold forconveying the solid state material along a conveying direction, aheating unit disposed downstream of the conveying unit along theconveying direction, and a molding unit, the heating unit including amain body, a nozzle disposed on a downstream side of the main body, anda heating channel extending through the main body and the nozzle forpassage of the solid state material therein, the molding unit includingat least two molds that cooperate with each other to define a formingspace, the nozzle having an injection port communicating with theheating channel; (E) activating the conveying unit for conveying thesolid state material from the eye mold to the heating channel; (F)heating the solid state material to melt a portion of the solid statematerial that is proximate to a forming space and become a liquid statematerial; (G) driving the solid state material that has not melted topush the liquid state material into the forming space; (H) cooling theliquid state material in the forming space to solidify the same into ablank; (I) debinding the blank for removing the binder material from theblank; and (J) sintering the blank to obtain a finished product.
 2. Themelt-molding metallurgical method as claimed in claim 1, wherein in step(A), the raw material powder is one of metal powder, glass powder andplastic powder.
 3. The melt-molding metallurgical method as claimed inclaim 1, wherein the solid state material in step (C) has a linear orrod shape.
 4. The melt-molding metallurgical method as claimed in claim1, wherein in step (F), the heating unit is activated to heat the solidstate material in the heating channel, and the portion of the solidstate material that is proximate to the forming space is melted to formthe liquid state material.
 5. The melt-molding metallurgical method asclaimed in claim 1, wherein in step (G), the solid state material thathas not melted is driven by the conveying unit to push the liquid statematerial so as to inject the liquid state material from the nozzle intothe forming space.
 6. The melt-molding metallurgical method as claimedin claim 1, wherein the molding unit in step (D) includes two moldsmated in an up-down direction, a lower one of the molds having aninsertion hole for insertion therein of the nozzle, the heating channelcommunicating with the forming space through the injection port.